1. Field of the Invention
The present invention relates to a clutch disc assembly for use in a clutch mechanism in a motorized vehicle where the clutch disc assembly is configured to allow for slight misalignment between a transmission input shaft and a flywheel of an engine.
2. Description of the Related Art
A clutch disc assembly used in a clutch mechanism in a motorized vehicle typically includes a pair of disc-shaped input plates, an output hub engaged with a flange in an outer periphery thereof, and an elastic member disposed so as to be compressed in a circumferential direction between the input plates and the output hub when the input plates and the output hub are rotated relatively. The input plate can be coupled to an engine flywheel, and a transmission shaft is inserted into a center of the output hub so as to be engaged with the output hub. The clutch disc assembly further includes a friction generation mechanism that produces a friction when the input plates and the output hub are relatively rotated.
Upon allowing torsional vibrations to be inputted to the clutch disc assembly thus organized, the input plates and the output hub are periodically rotated relatively through the elastic member, to thereby generate a hysteresis torque. As a result, the torsional vibrations are attenuated. The characteristics of a low rigidity (a wide twist angle) and a low hysteresis torque are preferable in order to attenuate the fine torsional vibrations.
The above-mentioned conventional clutch disc assembly also includes a bushing which is disposed in the inner peripheral edge of the input plates in such a manner that the bushing is abutted against the outer periphery of the hub, to thereby position the input plates with respect to the hub. It is very common for the transmission shaft to radially displaced or inclined with respect to the clutch disc assembly which is fixed to the flywheel of the engine, thus producing a slight misalignment. The hub being in engagement with the transmission shaft, is therefore radially displaced or inclined with respect to the input plates due to the misalignment of the shaft. However, because the hub cannot move radially with respect to the input plate, an unbalanced load is developed between the outer peripheral surface of the hub and the inner peripheral portion of the bushing. For that reason, when the transmission of the torsional vibrations makes the input plates and the hub rotate relatively, unwanted friction is produced between the bushing and the hub in response to relative rotation therebetween. As a result, the entire hysteresis torque is increased, and the fine torsional vibrations are transmitted to the transmission side without being absorbed by the clutch disc assembly, whereby a clack sound is liable to be generated in the transmission.
There also exists a clutch disc assembly of the separation type in which the conventional flange is separated from the hub to form a separated flange, and the separated flange and the hub are coupled to each other by a low-rigidity elastic member. In the clutch disc assembly of this type, a relative twist angle between the input plates and the hub is increased, and the clutch disc assembly exhibits two steps or levels of torsional characteristics, one level having a low rigidity and the second level having high rigidity.
In the friction generation mechanism, between one input plate and the respective separated flanges, the flange portion of the hub are disposed friction members which abut against the respective flanges and pressing members that presses the respective friction members against the corresponding flange portions. On the other hand, the bushing is relatively non-rotatably fitted to the inner peripheral end of the clutch plate. The bushing is abutted against the side surfaces of both the flanges. Also, the bushing is abutted against the outer peripheral surface of a boss, to thereby radially position the input plate and the hub.
In the above-mentioned separated-hub type clutch disc assembly, for example, there is a case in which the input plate is off-center with respect to the hub. In this case, an unbalanced load is developed between the outer peripheral surface of the hub and the bushing. As a result, the hysteresis torque in a range where the twist angle is small is increased, whereby the fine torsional vibrations cannot be effectively attenuated.